Canola Watch: Where did the plants go?

Got canola emergence issues?

Little canola plants are vulnerable to many different risk factors, including seedling diseases. Seed treatments are usually very good at managing the common seedling disease pathogens of canola, however seed, seedling and root rots can flare up under the right circumstances. Here are details about the three pathogens in the canola seedling disease complex, and the factors that tend to favour each of them.

Rhizoctonia solani. This pathogen causes the collapsed dead root tissue often called “wirestem”. We have two common groups of this pathogen on the Canadian Prairies. One group, which pathologists call AG2-1, likes it cold to cool, while the other group, AG4, likes it cool to warm. AG2-1 is the more common group in the Peace region. It can be active at soil temperatures as low as 2°C, and tends to be more severe when soils are moist and warmer than 2°C. Like root diseases in general, damage tends to be worse in heavy soils and compacted soils.

Fusarium species. Many different Fusarium species are active on canola seedlings. There is a high degree of variability among the species, but they tend to prefer warmer temperatures and moist soils.

Pythium species. Pythium likes saturated soil and is most active at soil temperatures of 5°C to 15°C. Pythium tends to be the first pathogen to infect canola, getting at the seed within three to five days of germination.

When scouting for the cause of poor emergence, check for the following symptoms of seed decay, stem rots and root rots that are all part of the seedling disease complex:

• Seeds fail to germinate and become soft and pulpy.
• Seeds germinate but the developing seedlings decay and fail to emerge.
• Seedlings emerge and appear normal above ground, but either the roots decay with rot moving rapidly up into the hypocotyl, or the young stem (hypocotyl) may be partially or completely girdled with decay. In this case, the young above-ground parts of the canola seedling may also wilt and exhibit a purplish or chlorotic discolouration. When the decay reaches the soil surface, the emerged part of the seedling topples over, wilts and dies.
• The hypocotyl appears constricted or shriveled and may be discoloured reddish brown. In moist topsoil, the shriveled stem may persist for a while, but in dry windy conditions, the whole seedling disappears in a few days. Seedlings may also emerge and then stagnate in the 2- to 4-leaf growth stage even when growing conditions appear favourable. Root hairs appear to be missing.

What else could it be? Seedling diseases are just one of many possible causes for missing canola plants. Insects, weather conditions, machinery issues are others. The full article has more details on these factors and more photos of seedling diseases.

 

In This Issue > QUIZ: Flea beetle risks Four questions that will help with your approach to flea beetle scouting and risk assessment. TAKE THE QUIZ > Tip 1: Finding time for sprayer tank clean-out With wind delays and pressure to get crops seeded, the weed spraying operation could be bouncing from crop to crop, and from pre-seed burnoff in one field to post-emergence in another. Crop safety requires attention to detail for tank mixing and sprayer clean-out. TIPS > Tip 2: Insects watch – cutworms and flea beetles Cutworm feeding results in notched, wilted, dead or cut-off plants. They can also leave whole patches of missing plants. Get a link to scouting tips in the Canola Encyclopedia. > Tip 3: Stuck? Extract that machinery safely Tow ropes and tow straps are intended for towing, not extracting. Recovery straps, typically made of nylon, can be utilized for extraction and, unlike chains and cables, can be jerked. See more tips and a great link. > Tip 4: Will a fertilizer top-dress pay off? Canola fields may benefit from a top-dress application of nitrogen or sulphur if logistics and weather prevented the full recommended application of fertilizer at or before seeding, and if improved weather conditions have increased the yield potential of the crop. > Tip 5: Broadcast seeding of canola In late springs with wet conditions, broadcast seeding may be the only way to get the job done on time. In some cases, broadcast seeding may actually provide better seed placement than “mudding in” seed with a drill. The Canola Encyclopedia has tips.